Method of making composite metal structure



July 30, 1968 E. VALYI 3,394,446

METHOD OF MAKING COMPOSITE METAL STRUCTURE Original Filed June 14, 19622 SheetS-Sheet 1 FIG -4 A TTORNEY July 30, 1968 E. l. VALYI 3,394,446

METHOD OF MAKING COMPOSITE METAL STRUCTURE Original Filed June 14, 19622 Sheets-Sheet 2 l/Z H4E S/v l FIG J5 A T TORNE Y United States Patent OMice 3,394,446 METHOD F MAKING CMPOSITE METAL STRUCTURE Emery I. Valyi,Riverdale, N.Y., assigner to Olin Mathieson Chemical Corporation, acorporation of Virginia Application Sept. 21, 1964, Ser. No. 398,127,now Patent No. 3,230,618, dated Jan. 25, 1966, which is a division ofapplication Ser. No. 202,612, `Tune 14, 1962, now Patent No. 3,201,858,dated Aug. 24, 1965, which is in tum a continuation-impart ofapplication Ser. No. 732,663, May 2, 1958. Divided and this applicationAug. 30, 1965, Ser. No. 499,129

8 Claims. (Cl. 29-157) ABSTRACT 0F THE DISCLSURE A method of making acomposite structure by providing a sheet metal member having a system ofinternal passageways therein bulging outfof at least one face thereofand metallurgically bonding a porous body at spaced points thereof tothe crests of the bulges.

This application is a division of copending application Ser. No.398,127, filed Sept. 21, 1964, now U.S. Patent 3,230,618, which in turnis a division of application Ser. No. 202,612, filed June 14, 1962, nowU.S. Patent 3,201,- 858. The latter application is in turn acontinuation-inpart of application Ser. No. 732,663, filed May 2, 1958,now U.S. Patent 3,049,795, which in turn is a continuation-in-part ofapplication Ser. No. 586,259, filed May 2l, 1956, now abandoned.

This invention relates to porous fabrications, and more particularly toa permeable body integrated to a supporting sheet metal structureadapted to conduct a fluid to the said permeable body for fiow anddistribution therethrough.

As brought out in the aforesaid co-pending applications, the subjectmatter thereof was directed to novel features wherein a permeable bodyformed of powdered metal is joined to a supporting metal structure so asto become integral therewith in all areas except where they are formedbetween the permeable and impervious portions of the structure.

The resultant porous fabrication may be utilized advantageously invarious applications. For example, it may be employed in the subsequentmanufacture of gas burners that are intended to provide evenlydistributed Iheat over large surfaces. AIn such application acombustible gas is distributed by the fluid channels to differentportions of the permeable body through which it flows to emanate on thecombustion side thereof substantially uniformly over most of the surfaceof that body at a substantially uniform rate, thus producing a flameblanket. The resultant porous fabrication may also be utilizedadvantageously in the construction of evaporative coolers whereby anefiicient cooling surface is obtained by using the porous metal body asa means through which to distribute over a large area the liquid whichis to evaporate for the purposes of transpiration cooling. ln a furtherapplication, the porous fabrication may be utilized in the constructionof filters wherein the porous metal body provides a controlled porosityand permeability so as to enable a liquid carrier to filter through theporous metal body while leaving filtrate on the other side thereof. Aswill be recognized, one of the most important limitations restrictingthe use of porous fabrications resides in the fact that it is verydifficult and costly to provide conduits which conduct fluids eicientlyto the appropriate faces or portions of the porous metal bodies, andtherefrom to be distributed into and through such porous metal bodies3,394,446 Patented July 30, 1968 for the purposes of combustion,evaporation, filtration, or other purposes. Another limitation of porousmetal bodies restricting their use in components designed to transferheat from one medium to another derives from the fact that the heatconduction of such porous bodies is less than that of solid metal bodiesand that it is difficult and costly to effect efficient heat transfer tothe porous bodies and through them. While the techniques and methods ofproducing pervious or porous bodies from powder metal have beenextensively discussed in the literature such as for example in PowderMetallurgy -by Dr. Paul Schwarzkopf (the MacMillan Company, New York,1947) and Powder Metallurgy edited by John Wulff (the American Societyfor Metals, Cleveland, 1942), no economical and efficient method hasbeen found thus far to overcome the limitations above referred to priorto the invention described in the aforesaid copending applications; thebasic concept of the contribution therein comprises the forming of anintegral structure of two or more metal layers of differingcharacteristics, of which at least one layer is porous and pervious tofluids, such as gases or liquids, and the others impervious and solid,these layers being secured together, preferably through a sinteringoperation, although brazing and other means may also be employed, so asto enable the formation of fiuid channels in predetermined portionsbetween the confronting faces of various layers comprising theintegrated porous structure.

In accordance with the disclosure of the aforesaid copendingapplication, the porous fabrication is formed from a supporting sheetmetal member which may have all or a portion thereof in the form of afiat, relatively thin plate, sheet, or strip. A pattern ofweld-inhibiting material is applied to this member in a designcorresponding to that desired for the fluid conducting channels whichare to be provided in the ultimate structure. Following the applicationof the weld-inhibiting material, a substantial layer of powdered metalaggregate is deposited upon the plate thus treated. Subsequent theretothis composite structure may be subjected to pressure to compact thepowdered metal and to press it firmly against the solid plate. Thiscompacted assembly is then exposed to a suitable sintering temperatureunder conditions preventing undesired reactions, such as oxidation ofthe metal. This sintering operation accomplishes the sintering of thepowdered metal particles to each other together with the metallurgicalbonding, welding, of the sintered metal aggregate to the solid member.

In an alternate method disclosed in the foregoing copending application,the powder metal layer may be separately formed by known powdermetallurgy techniques. 4In this method the solid sheet metal member maybe first prepared by applying a pattern of weld-inhibiting material tothe portions thereof at which the fluid channels are to be formed, andapplying to one side of the porous metal layer a suitable thin layer ofsoldering or brazing metal. The porous metal layer is then superimposedupon the solid plate so as to sandwich the weldinhibiting materialbetween them, and the composite subjected to a thermal treatment toaccomplish the brazing or soldering of the porous metal layer to thesheet metal member in all adjacent areas thereof except in thoseportions separated by the weld-inhibiting material.

The resultant composite structure may now be adapted for the conductingof fluids by deforming or tiexing tho-se portions of the sheet metalmember, which are disposed opposite the Weld-inhibiting material, awayfrom the porous metal layer. This can be accomplished for example byintroducing a iiuid under pressure into the ununited portions of thecomposite structure formed between the porous layer and a sheet metalmember, or mechanically, by insertion of suitable mandrels into theseareas. This deformation of the sheet metal member away from the porousmetal layer will form fiuid channels defined on one side by animpervious metal wall portion and on the other side by the porous metal.

As will be understood, various combinations of materials may be utilizedin forming the integrated composite structure; and accordingly the solidsheet metal member and the porous layer or body may be of the same metalor alloy, or the porous structure and the solid member, of theintegrated structure, may be comprised of different compositions. Forexample, both the porous metal layer and a solid sheet metal member maybe formed of the same stainless steels, coppers, brass, carbon steels,aluminum or various combinations thereof. As -will be understood theultimate use of the resultant integrated structure determines thespecific combination of alloys to be employed.

Accordingly, among the objects -of this invention is to provide meansfor fabricating novel porous metal structures adapted to distribute afluid and heat in How therethrough.

A further object of this invention is to provide a novelY method formaking porous metal structures adapted to distribute a fiuid and heat inflow threthrough.

Other objects and advantages of this invention will become more apparentfrom the following drawings and description in which FIGURE 1 is aperspective view of one embodiment of the present invention, withportions cut away, in a preliminary stage of fabrication;

FIGURE 2 is a sectional View along lines II-II of FIGURE l;

FIGURES 3 through 6 are sectional views similar to FIGURE 2 showingfurther embodiments in various stages of fabrication;

FIGURE 7 is a sectional view similar to FIGURE 2 showing a still furtherembodiment;

FIGUR-ES 8 and 9 are sectional views similar to FIG- URE 2 showing astill further embodiment in different stages of fabrication;

FIGURES 10 and 11 are sectional views similar to FIGURE 2 showing astill further embodiment in different stages of fabrication;

FIGURES 12 and 13 are sectional views similar to FIGURE 2 showing anadditional embodiment in different stages of fabrication;

FIGURES 14 and 15 are sectional views similar to FIGURE 2 showing anadditional embodiment in different stages of fabrication; and

FIGURE 16 is a sectional view similar to FIGURE 2 showing a stillfurther embodiment of the present invention.

In regard to production of the porous body, it may be obtained by the socalled gravity sintering method which comprises ta process whereingraded metal powder, frequently spherical metal powder, is poured bygravity into an appropriately shaped confined space, and usuallyvibrated to cause it to compact uniformly. As is obvious the choice ofparticle size of the metal powder will largely determine the amount ofporosity, i.e., void space. The metal powder or aggregate so packed isthen sintered in accordance with well-known metallurgy practices,producing a porous metal body whose bulk density, or apparent density,is but a fraction of the density of the metal or alloy from which thepowder particles are obtained. Generally, the conditions of vibrationand conditions of sintering are chosen to result in an apparent densityof approximately to 75% of the solid density of the cor-respondingalloys. In another procedure for the production of such porous metalbodies the process may comprise blending intimately a graded metalpowder with a combustible substance, such as for example wood fiour orother organic particulate material, or a soluble .'niaterial whosemelting point exceeds the sintering temperature of the metal powder.After the formulation of this dry blend, the mixture of metal powder andcombustible or soluble substance is then compacted under pressure, suchas by rolling resulting in a body that has no voids and is reasonablyfirm, sufficient for handling. This body is then sintered in accordancewith well-known powder metallurgy practices to produce a cohesivestructure in which the metal particles are sintered together at theirrespective points of contact and the combustible or soluble materialremains unbonded to the metal particles forming discrete islands withinthe metal body. Upon completion of the sintering operation and if thenonmetallic component is combustible, then the resultant body will infact contain void spaces everywhere previously occupied by thecombustible material since the latter will have burned away in thecourse of sintering. In the case utilizing a soluble material whosemelting point is higher than the sintering temperature of the metal, thesoluble material will remain intact after the final stages of sinteringand can be subsequently removed by leaching and dissolving with aliquid, lresulting in a network of interconnected pores.

In the modification of the foregoing it is noted the above described dryblend of metal powder and combustible or soluble substance may bereplaced, respectively, by a paste or slurry obtained by suspending theadmixed powder metal and combustible or soluble particles in a suitableliquid vehicle, as for example water or alcohol; or in applicationswhere the combustible substance is mostly organic, by choosing acombustible substance that is a viscous liquid instead of beingparticulate such as for example a liquid phenolic resin. Alternately,the mixture of metal powder and void or pore forming substance andvehicle, or void or pore forming substance alone, may be prepared into apaste which may be brought into the desired shape by pressing orextrusion.

A further method of producing the sintered porous metal bodies comprisesmelting a metal or alloy and casting it into the interstices of a porousaggregate of a particulate soluble material whose melting point exceedsthat of the metal. Upon solidification of the metal, a component isproduced which contains the network of the soluble material interspersedwithin the solid metal which soluble material is thereupon removed 'byleaching or dissolving, leaving behind it interstices that interconnectand form a porous network Iwithin the resultant metal body. Solublesubstances contemplated for these purposes, be it for blending withsolid metal powder or for the above casting process, comprise sodiumchloride in conjunction with aluminum and aluminum alloys, aluminumfluoride in conjunction with copper alloys, and calcium oxide inconjunction with alloys having melting points higher than copper alloys.As will be understood other substances, particularly inorganic salts,are readily available and known to the art such purpose as `for examplevarious phosphates, such as tri-sodium phosphate.

A still further method of producing a porous metal body comprisesweaving or knitting metal wire into a mesh arranged in a plurality oflayers. According to this process, a control of porosity is obtained byappropriate choice of wire diameters and openings arranged betweenadjoining wires as well as the juxtapositioning of superimposed layersof the woven or knit mesh.

Although a specific mass of sinterable metal has been described, it ispointed out that other formulations of sinterable materials may also beused, as for example those metal oxides, carbides and nitrides, ormixtures thereof, containing if necessary pore or interstice formingmaterials discussed above.

Various substances are known to be effective in preventing adhesion ofone metal body to another, even under severe pressure, as in rolling, atelevated temperatures, as in the course of soaking prior to rolling, ordiffusion-annealing, ctc. In fact, many substances present in metal asaccidental impurities, as for example manganese sulphide in steel,operate to produce seams and other discontinuities in rolled products.Among these su-bstances are graphite, applied for example in the form ofcolloidal suspensions, boron nitride, talcum, zinc oxide,

titania, and many others, each within certain limits of applicabilitythat are not relevant here. In fact, it has been noted that on occasionduring roll-welding of two superimposed sheets interference with theintegration oc curs even by the mere presence of an accidental oilsmudge on the surfaces of the sheets. For purposes of the presentinvention, the separation or weld-inhibiting materials employed need notwithstand exposure to high pressures or be capable of extending underpressure which normally are requisites of stopdweld resist used inpressure welding, Instead, the weld-inhibiting material employed as thespacer or supporting substance herein need only have reasonablemechanical strength to function as a spacer or support before thesuperimposed particulate material acquires strength of its own as thesintering operation progresses. The weld-inhibiting material employed asa spacer or supporting substance should preferably be capable of beingapplied at room temperature as a powder or by spraying, painting,extrusion, etc.; if needed, harden with the least time delay, and remainin place through the better part of the subsequent operations whichusually comprise the application of a loose particulate metal layer oftrans-porting the composite preparatory to a sintering operation and ofsintering. Moreover, this spacer or supporting substance must be capableof removal following the sintering operation even if the channel networkis extremely complex and tortuous.

Preferably the spacer or supporting substances contemplated herein areliquid soluble and have a lmelting point higher than the sinteringtemperature of the particulate metal layer, or at least higher than thetemperature at which that layer commences to acquire reasonablemechanical strength in the course of sintering. Such soluble substancesare for example sodium chloride, which melts at 801 C., a temperaturesomewhat belo-w the customary sintering temperature of copper; and itmay be used in connection with copper aggregate because the latter willacquire adequate strength during sintering before the sodium chloridebegins to melt. Other such soluble substances are sodium aluminate(melting at 1650 C.), potassium sulphate (melting at l076 C.), sodiummetasilicate (melting at 1088" C.), aluminum chloride (melting at 140C.), and others. The choice o-f such soluble spacer or supportingsubstances will of course also depend on possible solid phase reactionswith the metal surrounding them, at the temperatures of sintering. Forexample, while one of the most effective Weld-inhibiting lmaterialsadapted for use as the spacer or supporting substance in connection withcopper and aluminum alloys is graphite or carbon, austenitic stainlesssteel would be harmed by that spacer substance through carburizing.

In this respect it is pointed out that also contemplated within thisinvention is the utilization of a specific form of a carbon as aweld-inhibiting material in tne fabrication of these compositestructures. The particular form of carbon contemplated is that obtainedin situ, from organic substances, by pyrolysis. As is known, progressiveelevated temperature exposure of a variety of organic substances ininert or reducing atmospheres results in progressive thermal degradationof the organic rmaterial and ultimately in pyrolysis similar to coking.The residual carbonaceous matter is strong and cohesive as well asstable, except under oxidizing conditions at elevated temperatures. Theresultant weldeinhibiting material, originally introduced as an organicsubstance may thus maintain reasonable mechanical strength and itsfunctional integrity not only at room temperature but also throughoutthe process of heating during the sintering operation, while the powdermetal acquires appreciable strength and ability to support itself over apreformed channel forming the groove of the desired composite structure.However, the organic material applied to the solid metal surface orWithin the preformed channel of a solid metal member, may be used as aweld-inhibiting material `only if the carbonaceous residue remainingafter the sintering operation is removable. This in turn depends uponthe particular metal aggregate applied above it which -must be perviousand porous enough to permit the ambient atmosphere to react freely withthe contents of the channels. In such a case, the pyrolized organicsubstance will break down further and oxidize Without residue, if thesintering furnace atmosphere is adjusted to allow for progressiveformation of gaseous carbon compounds, or, as is Ipreferable, if exposedto air while still hot enough to oxidize vigorously.

For example, a paste-like mixture of silica sand and a phenolic varnishof the resol type may be used. The weld-inhibiting materials so formedcan be hardened at room temperature and then upon exposure to increasingtemperatures, will progressively harden and cure as is naturallyexpected for a phenolic resin, and thereafter progress through severalstages of heat degradation while heated to still higher temperatures inan inert atmosphere. In a specific application in which spherical copperparticles were metallurgically bonded to a copper sheet, during thecourse of the sintering operation the sand particles remained bondedtogether due to the carbonaceous residue of the phenolic resin. Uponremoval of the sintered composite from the furnace and while still at anelevated temperature approaching that of the furnace, but now exposed toambient air, the carbon oxidizes almost instantaneously leaving the sandfree flowing and devoid of any bond.

Oxidation of the pyrolyzed resid-ue may be accomplished usually by mereexposure to an atmosphere containing sufcient oxygen to burn the carbon,but not enough to oxidize lthe metal harmfully. In the case of copper,sintering may be followed by air exposure at room temperature, as abovedescribed; in the case of stainless steels, if brightness is to `bepreserved, cooling after sintering may take place in a protectiveatmosphere which may have just enough oxygen to react with the carbon. Awide variety of such Weld-inhibiting spacer and supporting substancesare readily available and known to the art; and in principle suchformulations usually consist of free flowing comparatively inertgranular materials, such as silica sand, bonded with phenolformaldehyde, urea-formaldehyde, polystyrene, polyethylene, furfuralformaldehyde, coal tar, etc., or such organic materials alone andothers, for example, paper, adhesive tape, etc., in the event tha-t onlythin films need to be applied prior to sintering.

As will be understood, the selection of materials from which the porousand solid components are made to comprise the structures describedherein and in the co-pending application, is based on considerationswithin the skill of persons acquainted with mechanical, physical andchemical properties of materials. While the structures described hereinhave been identified as being metallic on numerous occasions, it ispointed out that all or parts of these structures may be made ofnon-metallic materials, as called for by their intended use. Thus, theporous layer may incorporate catalysts, as pointe-d out in theco-pending application, which catalysts may be non-metallic. The porouslayer may also consist in part or entirely of glasses, carbides,nitrides, oxides, or borides, for example in instances calling for heatresistance, corrosion resistance or insulating properties not availablein metals and alloys. The porous layer may also consist of syntheticpolymeric substances, for similar reasons, as for example sinteredporous -iluoro-carbon resins, siilcone resins, and others. The solidcomponent is usually made of metal strip or plate which may be coatedwith non-metallic materials of the kind referred to. In instances notcalling for high strength the solid component may also be made ofsynthe-tic resins made into strip, sheet or plate stock.

Several of the embodiments described herein may be made a-dvantageouslyof non-metallic components. Thus, a component intended to distributehighly corrosive inorganic acid vapors may be made of fluorocarbonresins; another intended to serve as diffuser of combustible gas alsoacting as a radiant burner may be made in part of silicone carbide.Other examples are obvious to those skilled in the art of constructingcomponents to be used in environments of high temperature and corrosiveattack.

It will be understood that the porous layer referred to herein may beproduced in still additional ways either in situ, upon the surface of asolid component or separately, to be joined thereto. Thus, the porouscomponent may be produced by mechanical perforation of a solid metallicsheet; however, such a method would generally vbe expensive andcumbersome. The porous layer may also be produced by s praying of metalby techniques well-known to those skilled in the metal working art andcarried out either with a wire gun or a powder gun, whereby, throughappropriate and well-known adjustment ofthe spray gun, the spraying7process may be directed so as to produce a porous sprayed deposit. Aporous sprayed deposit may also be produced with a powder gun byspraying along with the material intended to form the porous layer andintimately intermingled with it an evanescent solid which will bedeposited along with the rest of the sprayed material and which may thenbe removed from the porous composite by leaching as described inprevious examples. However, this procedure of producing the porous layerby spraying is also cumbersome and expensive in most instances, comparedto the other means described herein and in the co-pending applications.

FIGURES 1 to 3 illustrate an embodiment of the present inventionutilizing for a, solid sheet metal member a sheet metal unit containinginternally thereof a pattern of fluid passageways such as obtained inaccordance with the process fully disclosed in a patent to Grenell,`U.S. Patent No. 2,690,002, granted on Sept. 28, '1954. According to themethod defined in this patent, a foreshortened pattern ofweld-inhibiting material 86 is applied to a clean surface of a secondsheet of metal is superimposed on this surface. These two sheets arethen secured to prevent relative movement between Ithem and are thenwelded together in the adjacent areas of the sheets which are notseparated by the weld-inhibiting material. Unification of the sheetsresults in an unjoined portion 86 between the outer surfaces of theunified sheet 87', which unjoined areas are distended by injectiontherein of a fluid pressure of suflicient magnitude tc permanentlydistend the blank in the area of the unjoined portion to form a -desiredpattern of passageways 88 which are defined by an oval configurationwhen expanded without external constraint of the expansion. Inaccordance with one method of this invention for fabricating the porouscomposite structures embraced therein, the distended structure 87 isthen adapted for the formation of the porous composite structure of thisinvention by positioning it between oppositely disposed containing walls289 adapted to confine the components to be superimposed on the face ofthe expanded unit 87. The troughs defined between the crest 89 of thebulges defining passageways y88 are filled with an evanescent material,such as the combustible or liquid soluble substances described above,followed thereon 4by superimposing thereon a compacted body ofparticulate granules, with the assembly thereafter bonded together inany appropriate manner as by sintering. Upon elimination of theevanescent material the particulate aggregate forms a sheet-likesintered porous body 90 bonded to the crests 89 of the bulges definingfluid passageways 88 contained within the sheet metal unit `87. Ifdesired each of the pair of opposite faces of the sheet metal unit 87may be provided with a sheet-like sintered porous metal body asillustrated in FIGURE 6. As shown therein a second sheet-like sinteredporous body 91 is superimposed on the external face of sheet metal unit87 and 8 bonded t0 the crest 92 of the distended bulges defining fluidpassageways 38.

Although the preceding embodiment was directed to internally laminatedsheet metal units freely distended into passageways defining bulges ofoval configuration, the invention is applicable where the distention isconstrained and restricted to any one side of the panel as illustra'tedin FIGURE 7 and obtained by methods similar to those disclosed in U.S.Patent No. 2,993,263. As illustrated herein an internally laminatedsheet metal unit 93 is constrained in its distention between flat rigidsurfaces permitting the distention to be restricted to only one side ofthe panel to form passageways 94tdened by bulges having flat topcrests95 to which is bonded a sheet-like metal porous body 96.

In accordance with another embodiment of this invention an internallylaminated sheet metal unit 97 adapted for distention is coated on one orboth of a pair of opposite faces, as in respectively FGURES 8 and 10,with a pattern of stop-weld material 98 applied in the design disposedin overlapping and staggered relationship with the internal laminationsof sheet metal unit 97. Thereafter a sheet-like sintered porous metalbody 99 is superimposed on the face of the sheet metal unit 97 coatedwith the weld-inhibiting material and the assembly subjected to asintering operation which causes the diffusion bonding between theporous metal body and the sheet metal unit in all areas except thosecovered by the weld-inhibiting material 98. The resultant composite unitis then subjected to a forming operation such as hydraulic inflationcarried out by injecting pressure fluid into the internal laminations ofthe solid sheet metal unit 97 only, resulting in the type of structuresillustrated in FIGURES 9 and 1l. That structure will be a tube sheethaving tube portions 161 interconnected by integral web sections 102wherein one or both faces of the tube sheet will have a sheet-likesintered porous metal body bonded to the crest of the tubes. As will beunderstood, in the course of forming, such as by hydraulic inflation asdescribed, the area of the original sheet corresponding to crest 103 ofthe tube sheet which adhered to the porous body 99 cannot be formedduring the distention of the internal laminations, therefore restrictingthe deformation to the portions 104 of the tubes whereby these portionsbecome stretched in course of hydraulic inflation while the porous metalbody remains almost completely unaffected. The resultant structureautomatically forms fluid channels between the solid sheet metal tubesheet and. the sintered porous metal layer. Thus, there is produced aunitary metal structure which has internal tubular passages in the solidmetal tube sheet, and an additional network of fluid channels betweenthe solid sheet metal tube sheet and the porous components, and ofcourse, an overall porous layer. In an alternate modification, shown inFIGURES 12 and 13, an internally laminated sheet metal unit 107 wassuperimposed on each of the opposite faces of a sheet-like sinteredporous body 166, sandwiching between all confronting faces a pattern ofweld-inhibiting material 168 in accordance with the foregoing. Uponjoining and distention, a composite results in which the sintered body106 has metallurgiically bonded to each of its opposite faces the crest109 defining the tubular passageways 110 of tube sheet 111.

FIGURE 14 in which the sheet metal unit 113 containing the laminations117 has the channels preformed by the groove-like indentations 116embossed within solid portions of the sheet metal unit 113 disposedbetween the laminations 117. These channels are thereafter filled with aspacer or supporting material, and a body of particulate metal powder11'8 applied over the sheet metal unit 113. Following the sinteringoperation and hydraulic inflation of laminations 117, a structure, suchas illustrated in FIGURE l5, is obtained in which a sheet-like sinteredporous body 115 is metallurgically bonded to the sheet metal unit 113 inall the regions except the ones juxtaposed over the fluid channels 114whereas the laminations 117 will have formed fluid passageways 112.

It is noted that some or all of these tubular passageways may serve toconduct uids or to impart rigidity to the overall composite structure ofboth. If it is desired to impart particularly high rigidity to thestructure then some of the tubular passageways 112 may be severed andthe sepa-rated sheet portions suitably turned into a crosssection havinga high section modulus such as shown in FIGURE 16, which again shows asheet-like sintered porous layer 115 superimposed and metallurgicallybonded upon a solid sheet metal unit 113 which contains altternatingfluid channels 114, closed uid passageways 112 contained within thesheet metal unit 113 and reinforcing ribs 119 formed from laminationssimilar to the ones developed into the fluid passageways 112.

Although the foregoing illustrates bonding of a porous metal layer toonly one side of the solid sheet metal unit 113, it will be obvious thatit may be provided on both sides or in preselected areas only ratherthan over the entire solid sheet metal unit. It is also readily possibleto superimpose several structures of this kind. As will also be evidentthe invention is susceptible to the production of intricate metallicstructures by layer-wise superimposition of several of theafore-described internally laminated units and subsequent hydraulicformation of the laminations contained therein. In accordance with thisinvention, it is moreover possible to interpose or sandwich between theporous components, and to alternate, layers of the internally laminatedsheet metal units with layers of porous metal whereby several channelnetworks are generated which may in principle be subdivided into one setof passageways entirely contained within the solid sheet metal unit andanother set of uid channels interposed between the solid sheet metalunit and the porous components.

As indicated above, the composite structures of this invention areadapted for many applications and particularly for use as heatexchangers. As is well known, tubular components used in heat exchangerswere heretofore usually provided with fins, corrugations and otherextensions of their surface so as to present an economic maximumextended surface area for a given weight of heat exchanger structure.However, such heat exchanger structures can be provided with greatlyincreased heat transfer surfaces by i.e. heat conductive bonding of asolid sheet metal unit to a sheet-like layer of sintered porous metal inaccordance with any of the methods described heretofore. As has beendiscussed the sheet-like porous metal component is attached to the solidsheet metal unit by a metallic bond which will warrant good heattransfer with channels provided between the confronting faces of thecornponents by interrupting the metallurgical bond in predeterminedareas and in a predetermined pattern. These channels serve to conduct afluid between the solid and porous layers with subsequent diffusion ofow through the porous body, thereby contacting the large surface areawithin the porous body, as defined by the innumerable intersticesextending between the integrated particles of the porous body. Forexample for application in refrigerator systems, where the solid sheetmetal unit is internally laminated with its laminations distended into asystem of fluid passageways, the fluid contained within the solid metalcomponent may be water and the iluid contained within the channels maybe liquid refrigerant or refrigerant vapor, as would be the case whensuch composite structures are used as refrigeration condensers orevaporators.

Although the invention has been described with reference to specificembodiments, materials and details, various modifications and changes,within the Scope of this invention, Iwill be apparent to one skilled inthe art and are contemplated to be embraced within the invention.

What is claimed is:

1. A method of making a sheet-like porous metal structure comprisingproviding an integral sheet metal member containing internally thereof apattern of unwelded areas distending said pattern into a correspondingsystem of fluid containing conduits bulging out of at least one face ofsaid unit, and metallurgcally bonding a porous body at spaced pointsthereof to the crest of said bulges to dispose portions of said bodybetween said points in spaced relationship to portions of said unitbetween said points.

2. The method of claim 1 wherein said bulges are provided with a at topconfiguration with said flat top forming said crest.

3. A method of making a sheet-like porous metal structure comprisingproviding an integral sheet metal member containing internally thereof apattern of unwelded areas, distending said pattern into a correspondingsystem of fluid containing conduits bulging out of at least one face ofsaid unit, filling the troughs defined by said bulges with stop-weldmaterial, superimposing a body of sinterable material comprisingparticulate metal aggregate on said face of said unit, sinteringtogether the contacting surfaces of said aggregate and said crest, andeliminating said stop-weld material.

4. The method of claim 3 wherein said bulges are formed with a at topconfiguration with said flat top forming said crest.

5. A method of making a sheet-like porous metal structure comprisingproviding an integral sheet -rnetal member containing internally thereofa plurality of unwelded areas adapted to be distended into acorresponding system of fluid conduits bulging out of at least one faceof said member with said conduits coextending with each other in spacedrelationship, distending1 said unwelded areas to form said system,applying stop-weld material to at least one face of said member instaggered and overlapping relationship to said conduits, metallurgicallybonding a sheetlike porous body to at least one face of said member atportions therebetween not separated by said stop-weld material, anddistending said unwelded areas into said conuits.

6. The method of claim 5 wherein said distention comprises positioningthe metallurgically bonded assembly between rigid surfaces coextendingwith the opposite faces of said assembly, with `said surfaces beingspaced apart a distance corresponding to the amount of distention to beimparted to said areas, and injecting fluid pressure into said areasunder sufficient pressure to distend said areas into said conduits.

7. A method of making a sheet-like porous metal structure comprisingproviding an integral `sheet metal member containing internally thereina plurality of unwelded areas adapted to be distended into acorresponding system of fluid conduits bulging out of a pair of oppositefaces of said member with said conduits coextending with each other inspaced relationship, distending said unwelded areas to form said system,applying stopweld material to each of said faces in staggered andoverlapping relationship to said unwelded areas, metallurgically bondingto each of said faces devoid of said stop-weld material a poroussheet-like metal body, and injecting into said unwelded areas a uidunder suiiicient pressure to distend said unwelded areas into saidconduits.

8. A method of making a sheet-like porous metal structure comprisingproviding an integral `sheet metal member containing internally thereofa plurality of un- Welded areas adapted to be distended into acorrespond ing system of fluid conduits bulging out of at least one faceof said member, applying stop-weld material to a face of said member instaggered and overlapping relationship to said unwelded areas,Isuperimposing on said face a sheet-like porous metal body so as tosandwich said stop-weld material between said face and one of a vpair ofopposite -faces of said body, superimposing on the other of saidopposite faces a second integral sheet metal member containinginternally thereof a plurality of unwelded areas adapted to be distendedinto a corre'- sponding system of conduits bulging out of at least oneface of said second member with the confronting faces of said body andsaid second member having stop-weld material disposed therein betweenlsaid faces in staggered and overlapping relationship with the unweldedaraes of said second member, metallurgically bonding together the`contacting faces of said Iirst and said second members and said bodytogether in the areas thereof not separated by stop-Weld material, andinjecting into the unwelded areas of `said tirst and second members afluid under sufficient pressure to distend all said unwelded areas intoa corresponding system of fluid conduits.

References Cited UNITED STATES PATENTS JOHN F. CAMPBELL, PrimaryExaminer.

P. M. COHEN, Assistant Examiner.

